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AJvYcCXNQlXuHAReal6LOGqf//9iZxHZ/yEr4vaPQZ3sFlVCepNJrw2IgjdD/0JvnL6mHaBDOXX5vCwX21o=@lists.xenproject.org X-Gm-Message-State: AOJu0YzH84NyjDzFFTXfdpeu3UC8oyQ93zGFCgzXa2uERBy3f/FQT7qh uP//D2vWeUx+K+vStCR1oVJrQC9VJK342yYCvzy5AmkBKpFWLJlSnly3xmWQsUU= X-Google-Smtp-Source: AGHT+IFUVRA8I6Ldlwxnk25/JsZh/aq4+qOA8XPhISve/6teXZ/JlPJ+2oj+wdriCabPCae/d41DYw== X-Received: by 2002:a17:907:9487:b0:a8d:caa:7fee with SMTP id a640c23a62f3a-a93a033804emr647560666b.7.1727348651041; Thu, 26 Sep 2024 04:04:11 -0700 (PDT) Message-ID: <4d9da48c-00ba-476d-8915-96ed765cdfbe@citrix.com> Date: Thu, 26 Sep 2024 12:04:06 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/5] xen/livepatch: drop load_addr Elf section field To: Roger Pau Monne , xen-devel@lists.xenproject.org Cc: Ross Lagerwall , Stefano Stabellini , Julien Grall , Bertrand Marquis , Michal Orzel , Volodymyr Babchuk , Jan Beulich References: <20240926101431.97444-1-roger.pau@citrix.com> <20240926101431.97444-2-roger.pau@citrix.com> Content-Language: en-GB From: Andrew Cooper Autocrypt: addr=andrew.cooper3@citrix.com; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 26/09/2024 11:14 am, Roger Pau Monne wrote: > The Elf loading logic will initially use the `data` section field to stash a > pointer to the temporary loaded data (from the buffer allocated in > livepatch_upload(), which is later relocated and the new pointer stashed in > `load_addr`. > > Remove this dual field usage and use an `addr` uniformly. Initially data will > point to the temporary buffer, until relocation happens, at which point the > pointer will be updated to the relocated address. > > This avoids leaking a dangling pointer in the `data` field once the temporary > buffer is freed by livepatch_upload(). > > Note the `addr` field cannot retain the const attribute from the previous > `data`field, as there's logic that performs manipulations against the loaded > sections, like applying relocations or sorting the exception table. > > No functional change intended. > > Signed-off-by: Roger Pau Monné Reviewed-by: Andrew Cooper > diff --git a/xen/common/livepatch.c b/xen/common/livepatch.c > index df41dcce970a..7e6bf58f4408 100644 > --- a/xen/common/livepatch.c > +++ b/xen/common/livepatch.c > @@ -371,18 +371,21 @@ static int move_payload(struct payload *payload, struct livepatch_elf *elf) > > ASSERT(offset[i] != UINT_MAX); > > - elf->sec[i].load_addr = buf + offset[i]; > + buf += offset[i]; > > /* Don't copy NOBITS - such as BSS. */ > if ( elf->sec[i].sec->sh_type != SHT_NOBITS ) > { > - memcpy(elf->sec[i].load_addr, elf->sec[i].data, > + memcpy(buf, elf->sec[i].addr, > elf->sec[i].sec->sh_size); > dprintk(XENLOG_DEBUG, LIVEPATCH "%s: Loaded %s at %p\n", > - elf->name, elf->sec[i].name, elf->sec[i].load_addr); > + elf->name, elf->sec[i].name, buf); > } > else > - memset(elf->sec[i].load_addr, 0, elf->sec[i].sec->sh_size); > + memset(buf, 0, elf->sec[i].sec->sh_size); > + > + /* Replace the temporary buffer with the relocated one. */ > + elf->sec[i].addr = buf; I'd suggest /* Update sec[] to refer to its final location. */ Replace is technically the memcpy() above, and "relocate" means something else in ELF terms. Can fix on commit.